1. Field of the Invention
The present invention relates to a magnetic core for a signal line filter which is adapted to be attached to a connector at a signal line cable terminal portion for connecting electronic devices to thereby form a signal line filter and to absorb noises transmitted through the signal line cable from the inside or the outside of the electronic devices.
2. Discussion of Background
There has been known, as a method of absorbing noises transmitted through the signal line cable, a technique to absorb such noises wherein a magnetic core such as ferrite or the like with a number of holes is connected to a terminal connector for the signal line cable to absorb noises by utilizing the high impedance characteristics possessed by the magnetic material.
FIG. 4a is a plane view showing a conventional magnetic core for a signal line filter, which is adapted to be attached to a connector, and FIG. 4b is a cross-sectional view taken along a line A--A view in FIG. 4a. A magnetic core 1 made of a magnetic substance such as ferrite or the like is provided with a large number of pin insertion holes 2 in the direction of thickness of the magnetic core. FIG. 5 is a cross-sectional view of the conventional magnetic core taken along a line B--B in FIG. 4a, which is attached to a connector to thereby form a signal line filter. In FIG. 5, reference numeral 3 designates a signal line filter in which connector pins 5 of a signal line connector 4 are inserted in the pin insertion holes 2 of the magnetic core 1. In the case that noises transmitted through the signal line cable are absorbed by using the magnetic substance such as ferrite or the like, the magnetic core 1 having the pin insertion holes 2 whose number is the same as that of the connector pins 5, is attached to the connector 4 at a signal line cable terminal portion so that a high impedance is produced. Since the impedance functions as a resistance component against a noise current, the magnetic core 1 absorbs the noises and discharges the noise energy as heat, whereby it serves as a signal line filter.
Thus, the signal line filter 3 is constituted by assembling the magnetic core 1 in the signal line connector 4. However, there has been a demand for miniaturizing the connector 4, with the result that the pitch between the connector pins 5 is small. Further, there has been tendency that the magnetic core is assembled in the connector having a large number of pins. Accordingly, it has been not easy to attach the magnetic core 1 to the connector 4. Therefore, it has been necessary to enlarge, as a whole, the diameter of the pin insertion holes 2 in order to facilitate the attachment of the magnetic core to the connector 4. As a result, there arose a problem that the noise absorbing effect became inferior.